Thermodynamic analysis of phase diagram of H2O-DMF-PCL system: investigation on the influence of inorganic additives TiO2/MMT

Phase diagrams for H2O-DMF-PCL ternary system and with the presence of inorganic additives, H2O-DMF-PCL-(TiO2/MMT) quaternary system are studied using Flory-Huggins theory, which explains the thermodynamic behavior of polymeric membranes formed out of phase inversion process. The experimental binodal curves were plotted using cloud points obtained from the titration method. Also, the experimental spinodal curve was drawn using the compositions at the onset of phase separation in the titration method and found matching with the theoretical spinodal curve. The effect of variations in the interaction parameters on the location of the binodal curve is studied. The ternary interaction parameter was determined by fitting the binodal curve with the cloud point data for the ternary and quaternary system. The interaction of PCL-DMF-H2O is found to be consistent even in the presence of TiO2 or MMT. Also, the ternary and quaternary interaction parameters involving these additives were found to be negligible within the system. On the other hand, the presence of additives shifted the binodal curve toward the solvent-polymer axis manifesting the less requirement of non-solvent for phase separation. The critical point for the ternary system obtained in both experiment and theoretical calculation was at the polymer concentration of around 6 wt%. Membranes having composition above the critical point were synthesized using phase inversion technique, and their morphology was examined using SEM images.